Retinoid receptor subtype-selective modulators through synthetic modifications of RARγ agonists

A series of retinoids designed to interfere with the repositioning of H12 have been synthesized to identify novel RAR gamma antagonists based on the structure of known RAR gamma agonists. The transcriptional activities of the novel ligands were revealed by cell-based reporting assays, using engineered cells containg RAR subtype-selective fusions of the RAR ligand-binding domains with the yeast GAL4 activator DNA-binding domain and the cognate luciferase reporter gene. Whereas none of the ligands exhibited features of a selective RAR gamma antagonist, some of them are endowed with interesting activities. In particular 24a acts as a pan-RAR agonist that induces at high concentration a higher transactivation potential on RAR alpha than TTNPB and synergizes at low concentration with TTNPB-bound RAR alpha but not RAR beta or RAR gamma. Similarly, 24c synergizes with TTNPB-bound RAR gamma and exhibits RAR alpha,beta antagonist activity. Compounds 24b and 25b are strong RAR alpha,beta-selective antagonists without agonist or antagonist activities for RAR gamma. Compounds 24b and 24c display weak RXR antagonist activity. In addition several pan-antagonists and partial agonist/antagonists have been defined. (C) 2009 Elsevier Ltd. All rights reserved.